US Senate(WASHINGTON) — The Republican chairman of the Senate Judiciary Committee says his party can’t obstruct Hillary Clinton’s Supreme Court pick if she wins the presidency.

Speaking to reporters Tuesday, Grassley, who is running for reelection, pushed back against Sen. John McCain’s suggestion on Monday that Republicans would be “united” against Clinton’s Supreme Court nominee.

“If that new president happens to be Hillary, we can’t just simply stonewall,” Grassley said.

Grassley and other Senate Republican leaders have not considered President Obama’s nominee, Merrick Garland, to replace the late Justice Antonin Scalia, insisting that the vacancy on the nation’s highest court should be filled by the next president.

“I think we have a responsibility to very definitely vet … whoever nominee that person puts forward. We have the same responsibility for Trump,” Grassley said.

“We will very clearly vet … and once that’s done make a decision whether we’ll vote for or against,” he continued.

Progressive groups and Grassley’s opponent, Democrat Patty Judge, have criticized the Iowa senator and other Republicans for refusing to act on Garland’s nomination.